EctoVerb - reverb imitation from 2 PT2399s!!

[BluffChill]

I love reverb effects but buying Belton Bricks gets pretty expensive, so I've designed an imitation reverb using 2 PT2399s.

There's one control - mix, but you can use pots to change the feedback amounts for each PT2399.

I think it's a pretty decent emulation and sounds quite warm and lo-fi, a little bit like a cross between a spring reverb and an oil can delay almost. I'm having one problem with it - it hisses a little bit and I'm not sure what I can do to tame it. Anyone have any ideas?

Full development blog with sound samples and schematic here:

http://bluffchilldevices.blogspot.com/2018/08/the-ectoverb-low-cost-belton-brick-free.html



I've ordered a prototype run of some boards - all being well, these will be for sale and I'm thinking of doing a few one-off builds too.

[Kipper4]

You could try moving the filter on the output.
Maybe filter the ptxxxx output at a different place than after the mix pot.

You might be able to filter the dc biasing on the 2n5457 gate.
Search noiseless biasing.
It might make a difference but in noise reduction.

Furthermore you might be able to get rid of the 2x 2M and use the regulators 5v signal with a series R.

[samhay]

The delays are both quite short, so the noise performance has the potential to be pretty good
Suggestions:
You can take the input from the Q1 source.
You can then make most of the resistors around the PT2399s 10-100x smaller.
You could also use 2-pole filters to roll off more of the treble as per the application note.
C10 and C12 can be 100n, which also helps with noise.

Merlin / valvewizard designed a couple of 2 PT2399 reverbs. I think one put them in parallel. Can't remember which one he preferred. Look for the 'Solstice' and 'Equinox' circuits, which he posted here.

[PRR]

> it hisses a little bit

R1 and related NFB network sure are high enough resistance to hiss at guitar level. You can't make that smaller?

THEN it will load-down the gitar. Move the feed for R1 to the JFET buffer. Even use an opamp buffer.

[BluffChill]

Thanks for your suggestions folks. I'll do some twiddling. The only reason I didn't take the input to the delay chip from the source is because the PT2399 has a nasty habit of distorting with too high an input (2.5v)

[samhay]

Q1 has a voltage gain of slightly less than 1.
Unless your guitar is super high impedance, you should have a very similar signal voltage hitting the PT2399.
If this is a problem, you can configure the buffer around the first PT2399 to have a gain < 1.

[stringsthings]

Bluff, 

Nice work!

[ did anyone verify the vero of the Red Rabbit Fuzz? ]